Copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) are commonly referred to as fluorinated ethylene-propylene (FEP) resins. The HFP content usually ranges between about 10 and 20 weight percent (wt %). The FEP resins are melt-processable, having a melt viscosity adequate for conventional melt processing. However, FEP does not exhibit the high temperature properties and thermal stability of PTFE. Depending on their HFP content, these resins have a crystalline melting point from about 250 to 270° C., and have a maximum use temperature of around 200° C. Typical applications include wire insulation and molded parts.
Copolymers of TFE with perfluoro (propyl vinyl ether) (PPVE) are commonly called perfluoroalkoxy (PFA) resins. The PPVE content usually ranges between about 2 and 10 wt %. The PFA resins generally have better thermal stability and better mechanical properties at high temperatures when compared to FEP resins. The PFA resins are also melt-processable with a crystalline melting point from about 300 to 310° C., and they have properties similar to PTFE. Typical applications include expansion joints and liners for pipes and fittings, tubing, and film. Equipment made from PFA is used extensively in the semiconductor industry for demanding chemical handling applications.